As high performance aircraft become more and more complex, the need for more extensive and specialized training also increases. To obtain such training the student pilot must either be provided with actual training and experience in the aircraft which he is to pilot, or be provided training in a simulator of the aircraft. Training in the actual aircraft simply cannot be accomplished with respect to certain emergency procedures and maneuvers because of the dangers of the actual or real life environment. This is, of course, especially true for single pilot aircraft. Further, as fuel becomes more and more expensive, the time required to set up a training environment makes such training costs excessive even without considering the actual wear and tear of the aircraft. Consequently, because of the versatility, low operating costs, and lack of inherent dangers, aircraft simulation is being called upon to take over more and more of the aircraft training missions. However, to be truly effective, the aircraft simulator must faithfully represent or reproduce the environment that the trainee or student pilot would face in an actual flight.
Over a short period of time, flight simulators have developed from the early bellows driven Link trainers to todays highly sophisticated, computer controlled, flight/mission simulators. With ever increasing versatility and fidelity, todays simulators duplicate a broad spectrum of flight conditions and aircraft performance in both normal and malfunction modes. By employing the advanced motion systems, a multitude of digital computers, visual displays and the like, present day simulators are able to generate and integrate a multiplicity of realistic flight cues used to provide effective training for flight crew members. However, as will be appreciated by those familiar with the art of teaching, it has been found that the more senses of an individual that can be directed towards a problem, the faster and more thoroughly he learns. Thus, all cues that a pilot experiences in flying an aircraft must be properly and effectively simulated. Perhaps the most important cues that a pilot depends upon are visual cues. To this end, many if not most modern aircraft simulators employ some type of visual system to provide these visual cues, and over the years almost every imaginable system for providing a realistic dynamic visual scene has been used.
There are various types of scene generation systems which are used with modern vehicular or aircraft simulators and these include motion film projection systems, camera model systems, and digital image generation systems. However, experience has shown that the more acceptable systems used today, are substantially limited to camera model systems such as described in U.S. Pat. Nos. 2,975,671; 3,643,345; 3,670,426 and 3,961,133, and computer generated image systems, such as those systems described in U.S. Pat. Nos. 3,621,214; 3,826,864 and 3,961,133.
It will be appreciated by those skilled in the art, that the generation of a visual scene from digital data first requires the digitizing of every feature in the scene that is to be shown. Providing a dynamic visual scene suitable for use on an aircraft simulator which is unrestricted in its position, altitude, and attitude (within geographical limits, of course) perhaps presents the most difficult problems of all for computer generation. These problems include features to present, as well as the respective position of each feature with respect to every feature that is to be illustrated on the display screen. Various techniques have been developed to accomplish this task. To those knowledgable in the field of computer image generation and the use of computer image generation in aircraft simulation, it will be appreciated that one of the most successful techniques of solving the myriad of tasks associated with computer image generation is the use of a visual pyramid representing the entire FOV (field of view) of the aircraft pilot. A complete description of this technique is available by referring to U.S. Pat. Nos. 3,621,214 issued to George W. Romney et al.; 3,639,736 issued to Ivan E. Sutherland; and 3,889,107 issued to Ivan E. Sutherland.
However, even though the basic techniques for providing dynamic computer generated images are well known to those skilled in the art, there are still problems associated with computer image generated visual scenes which distract from the realism of such a scene. For example, determining exactly when to process and introduce a feature in a dynamic visual scene is not simple and straight forward. In particular, it will be appreciated that some features such as a mountain are very large while another feature such as a building might be relatively small. Therefore, it is clear that the "mountain" in the flight path must be introduced in the dynamic visual scene long before the building. However, as the aircraft continues to move along the flight path and moves closer and closer to the building, even details of the building may (or should) become visible. Thus, a technique or "criteria" to determine when a feature is to be introduced must be established. Unfortunately, establishing the appropriate criteria also presents problems. For example, if a minimum size is the only criteria, and a size just small enough to be perceptable is choosen as the minimum size, then there is often the very disturbing occurrence of the feature scintillating or blinking in and out of the view. On the other hand, if the computer does not generate the feature until the size of the feature is so large that it will clearly always be visible to the pilot, the sudden "popping in" of a feature that was not present earlier is also very disturbing, and, of course, unrealistic.
Therefore, it is an object of the present invention to provide methods and apparatus for producing a signal representing the correct instantaneous amount of blending needed to blend a selected feature into a dynamic computer image generated scene which avoids the scintillation and "pop in" effect.
It is another object of the present invention to provide methods and apparatus which allows a selected feature to be blended into a computer generated scene at a shorter range without the feature seeming to "pop in" to the scene.
It is yet another object of the present invention to provide methods and apparatus for blending selected features into a dynamic visual scene and for determining the processing load of a computer image generation system.